Dead AUX battery

[eltaco]

Some of you will know that I’ve been having instrument cluster issues for a long while now. Those have been relatively minor blackouts which occur on startup only. The display blacks out, truck beeps, and then it restarts and we’re all good to go again. Again, this only happens on startup.

I’ve been seeing a significant uptick in these events where now it’s happening every other start of the truck or so. Well, this weekend I ended up having a dead battery… maybe a clue?

This is where it gets a bit weird to me. I put the truck on a NOCO 5A charger and let it sit for 2 full days, and the NOCO was still showing under 25% charge. I had it connected only to the main battery, which was dead as could be. After this I used a jump start device this morning and got it to fire up on the 2nd try. Brought it into the dealer and they did a full recharge and test on both batteries. To my surprise, I’m told ONLY the auxiliary battery has failed, but the main battery is still healthy.

I’m struggling to make sense of this since the main battery also died overnight and I couldn’t get it to take a charge.

I’m no electrical expert, so just wanting to learn if this is sensible. Anyone else run into ONLY an Aux battery failure?

 

[Milchuck]

Some of you will know that I’ve been having instrument cluster issues for a long while now. Those have been relatively minor blackouts which occur on startup only. The display blacks out, truck beeps, and then it restarts and we’re all good to go again. Again, this only happens on startup.

I’ve been seeing a significant uptick in these events where now it’s happening every other start of the truck or so. Well, this weekend I ended up having a dead battery… maybe a clue?

This is where it gets a bit weird to me. I put the truck on a NOCO 5A charger and let it sit for 2 full days, and the NOCO was still showing under 25% charge. I had it connected only to the main battery, which was dead as could be. After this I used a jump start device this morning and got it to fire up on the 2nd try. Brought it into the dealer and they did a full recharge and test on both batteries. To my surprise, I’m told ONLY the auxiliary battery has failed, but the main battery is still healthy.

I’m struggling to make sense of this since the main battery also died overnight and I couldn’t get it to take a charge.

I’m no electrical expert, so just wanting to learn if this is sensible. Anyone else run into ONLY an Aux battery failure?

Just from lurking in the RHO forums, it seems like it's relatively common for the aux batteries to go bad first which then causes it to leech from the main battery until failure.

 

[rpr]

I would start the truck and take a DMM voltage reading off both batteries. They should both show 13.6V+ if they’re both getting a charge from the alternator.

If the Aux battery is below that but the main battery is above that you’re a victim of the infamous blown 150A fuse in the fuse array beneath the PDC. That fuse cuts the charging circuit from the alternator to the aux battery and it brings down the main battery with it.

 

[eltaco]

I would start the truck and take a DMM voltage reading off both batteries. They should both show 13.6V+ if they’re both getting a charge from the alternator.

If the Aux battery is below that but the main battery is above that you’re a victim of the infamous blown 150A fuse in the fuse array beneath the PDC. That fuse cuts the charging circuit from the alternator to the aux battery and it brings down the main battery with it.

Thanks, that’s good info.

The truck is currently at the dealer so I’ll ask if that’s something they’ve looked at.

Just one thing… what’s a PDC?

 

[RamFan]

Thanks, that’s good info.

The truck is currently at the dealer so I’ll ask if that’s something they’ve looked at.

Just one thing… what’s a PDC?

Power distribution channel? It’s the main fuse box

Chris

 

[rpr]

Power Distribution Center, main fuse box under hood, PDC is how the manual and my dealer refer to it.